Conventionally, an azimuth sensor which detects the earth magnetism to determine an azimuth has employed a Hall element having a high sensitivity for detecting the weak earth magnetism. Hall elements of this type include a conventionally well-known Hall element adapted to detect a magnetic field component perpendicular to a substrate surface (i.e., chip face), and a vertical Hall device adapted to detect a magnetic field component horizontal to a substrate surface (i.e., chip face).
FIG. 1 is a schematic view for illustrating a conventional vertical Hall device. The Hall element, which is described in Patent Document 1, includes a semiconductor substrate layer 11 composed of p-type silicon, and an n-type semiconductor region (n-well) 12 formed as a diffusion layer (well) by doping a substrate surface with an n-type conductivity impurity. P-type diffusion layers (p-wells) 14 are located adjacent to the semiconductor region 12 for device isolation of the Hall element from other Hall elements. The p-type diffusion layers 14 are formed so as to be surrounded by the semiconductor substrate layer 11.
As the impurity concentration in the semiconductor region 12 becomes lower (i.e., thinner), the carrier mobility in this region becomes higher. For this reason, in order to increase the sensitivity of the Hall element as a magnetic sensing element, that is, in order to obtain a higher voltage as an output voltage, it is desirable that the impurity concentration in the semiconductor region 12 be lowered (i.e., thinned). Accordingly, the impurity concentration in the semiconductor region 12 is set to fall within a range of 1.0×1014/cm3 to 1.0×1017/cm3 for example.
Contact regions (n+ diffusion layers) 13a, 13d and 13e are located in a region (active region) of the surface of the semiconductor region 12 which is surrounded by the diffusion layers 14 in order to increase the impurity concentration (n-type) in the surface selectively.
Patent Document 1: Japanese Patent Laid-Open No. 2005-333103
Any one of the azimuth sensors that have been developed so far comprises a magneto-resistance element, a flux gate, or the like which is based on a principle different from the Hall effect. For this reason, a signal processing chip and the azimuth sensor have been required to be placed in separate arrangements, thus making the construction complicated. Though it has been desired to develop an Si monolithic azimuth sensor, the insufficient S/N ratio due to a low sensitivity of an Si Hall element has precluded the practical use of such an Si monolithic azimuth sensor.
The conventional Hall element shown in FIG. 1, wherein the surface of the semiconductor substrate layer 11 is doped with the n-type conductivity impurity, which in turn is diffused to form the semiconductor region 12 as a diffusion layer (i.e., well), enables a substrate layer of a single conductivity type to be used as the semiconductor substrate layer of the Hall element and hence achieves the effect of enhancing the degree of freedom in selecting a substrate layer to be used in the formation of the Hall element.
However, problems have still remained until a low-concentration n-well is used within a suitable range as in the present invention to realize a Hall element which has a high sensitivity and contributes to an improvement in S/N ratio per current, and to realize a Hall element having a high breakdown voltage and high reliability. Further, the conventional Hall element has not been contrived to reduce the junction capacitance around a magnetic sensing part so that the element becomes less susceptible to noise caused by coupling.
The present invention has been made in view of such circumstances and, accordingly, an object of the present invention is to provide a Hall element and a magnetic sensor which have a high sensitivity and contribute to an improvement in S/N ratio per current by limiting a low-concentration n-well within a suitable range.